Presently, communication networks, which are typified by the Internet, have become widespread in society. Accordingly, various services targeting users of information processing terminals (hereinafter, referred to as “terminals”) connected to communication networks have been provided using information processing device (hereinafter referred to as, “servers”).
The server providing services generates a session in response to a request message received from the terminal, and provides the service targeting a user of the terminal. The session corresponds to a unit according to which the server provides a service for one terminal. The server having generated the session inserts a session ID, which is an identifier for identifying the generated session, into a message (response) for responding the terminal, and transmits the message. Subsequently, the terminal having received the message, into which the session ID has been inserted, transmits this message with the session ID inserted thereinto to the server. This allows the server to continue to provide the service by means of the session ID in the message received from the terminal.
In a case of performing a process of relaying a communication between the terminal and the server using the content of the message, a processing load on the relay device becomes high. There is a scale-out scheme, which is an example of a method used for the sake of improving the throughput of the relay process. The scale-out scheme improves the processing capacity of the relay system by arranging CPUs and causing the CPUs to perform parallel processing.
FIG. 1 is a diagram for illustrating a relay system adopting the scale-out scheme. The relay system includes a plurality of relay devices 3 (3-1, . . . , 3-n). In FIG. 1, an L4-server load balancer (L4-SLB) 5 is arranged upstream from the parallel arranged relay devices 3 (3-1, . . . , 3-n). The L4-server load balancer 5 performs a process that refers to the L3 header or the L4 header of each of packets and distributes the packets among the relay devices 3. The relay device 3 performs a process that constructs a message out of the packet, refers to the session ID to determine the forwarding destination of the message and transmits the message.
When the packet is distributed, the L4-server load balancer 5 does not refer to the session ID. Accordingly, request messages including the identical session ID do not necessarily reach the relay device 3 having previously been used.
The relay device 3, having relayed the first request message and response message, holds information (forwarding destination information) including the session ID and the server address as the message forwarding destination that corresponds to the session ID.
On the other hand, the other relay devices 3 fail into a state without the forwarding destination information. In this state, the relay devices 3 are incapable of delivering a request message issued by the terminal 1 to the server 2 having session data. Accordingly, the parallel arranged relay system includes a mechanism of synchronizing forwarding destination management tables 4. When a session is established, the forwarding destination information is synchronized among the relay devices 3. This allows the subsequent message to be successfully forwarded to the corresponding server even if this message is assigned to any relay device. It can be considered that there are two methods of synchronizing a forwarding destination management table, for example, as depicted in FIG. 2 and FIG. 3.
FIG. 2 depicts the first synchronization scheme of forwarding destination management table. The first synchronization scheme of the forwarding destination management table is a scheme that synchronizes items of (forwarding destination information) of the forwarding destination management tables 4 (4-1, 4-2, . . . , 4-n) among the relay devices 3 (3-1, 3-2, . . . , 3-n). According to this method, the forwarding destination information is distributed from the relay device 3 having relayed the initial request and response messages including a specific session ID, to the other relay devices 3.
FIG. 3 depicts the second synchronization scheme of the forwarding destination management table. The second synchronization scheme of the forwarding destination management table is a scheme that provides a forwarding destination setting mechanism 7 outside the group of relay devices 3. The forwarding destination setting mechanism 7 distributes the forwarding destination information to each relay device 3. The forwarding destination setting mechanism 7 collects information on the server address for holding the session ID and the session data from the server 2 when the session is established. The forwarding destination setting mechanism 7 generates the forwarding destination information on the basis of the collected information, and directs this information to each relay device 3.
Since the forwarding destination information in the relay devices can thus be synchronized thereamong, the relay device 3 is capable of directing a request from the identical terminal 1 to the identical server 2-1 during the session is maintained (uniqueness assurance).    Patent Document 1: Japanese Patent Laid-Open No. 2001-526814    Patent Document 2: Japanese Patent Laid-Open No. 2010-108479